This invention relates generally to gas turbine engines and more particularly to compressor stators used in such engines.
A gas turbine engine includes a compressor typically including a plurality of axial stages that compress airflow in turn. A typical axial compressor includes a split outer casing having two 180 degree segments that are suitably bolted together at axial splitlines. The casing includes rows of axially spaced apart casing slots that extend circumferentially therearound for mounting respective rows of vane segments or sectors.
A typical vane sector includes radially outer and inner bands between which are attached a plurality of circumferentially spaced apart stator vanes. The outer band includes a pair of axially spaced apart forward and aft rails, which are typically L-shaped with corresponding forward and aft hooks. The casing includes complementary forward and aft grooves that extend circumferentially within each of the casing slots for receiving the corresponding rails in a tongue-and-groove mounting arrangement.
During assembly, the individual vane sectors are circumferentially inserted into respective ones of the casing halves by engaging the forward and aft hooks with the corresponding forward and aft grooves. Each vane sector is slid circumferentially in turn into the casing slot until all of the vane sectors in each casing half are assembled. The two casing halves are then assembled together so that the vane sectors in each casing slot define a respective annular row of adjoining sectors for each compression stage.
A conventional compressor rotor having corresponding rows of compressor blades is suitably disposed within the compressor stator. Conventional sealing shrouds or segments are suitably attached to the radially inner bands of the vane sectors to cooperate with labyrinth teeth extending from the compressor rotor for effecting interstage seals.
In this configuration, the individual vane sectors are mounted to the outer casing solely by their outer bands, with the vanes and inner bands being suspended therefrom. The tongue-and-groove mounting arrangement therefore requires suitable clearance for not only allowing assembly of the vane sectors, but for also allowing differential thermal expansion and contraction between the components during operation of the compressor.
Typical manufacturing tolerances and stack-up thereof create clearances or gaps between the outer bands and the casing. During operation, air is compressed in each of the compressor stages and effects tangential and axially forward resultant aerodynamic loads acting on the vane sectors. The axial load urges the vane sectors forwardly and is reacted by axial engagement between the forward rail and the forward side of the casing slot, while increasing the axial gap between the aft side of the casing slot and the outer band. The tangential load is reacted by a typical anti-rotation key disposed in the casing slot at a casing splitline.
Since the compressor rotor excites vibratory response of the vane sectors during operation, and the vane sectors experience differential thermal expansion and contraction relative to the casing, the interfacing components thereof are subject to vibratory and thermal movement which may cause frictional wear. In order to reduce such frictional wear, conventional wear coatings or wear shims are provided. However, the coatings and shims are also subject to typical manufacturing tolerances and stack-up clearances, and do not abate the underlying frictional wear mechanism.
A useful approach to remedying this wear problem is described in U.S. Pat. No. 5,846,050 issued Dec. 8, 1998 to Jan C. Schilling. The Schilling patent discloses a seating spring for a compressor vane sector. The seating spring includes a reaction tab configured to abut the compressor casing on one side of the casing slot. At least one resilient spring arm is fixedly joined to the reaction tab and is configured to abut one of the outer bands so as to bias that outer band against the casing on an opposite side of the casing slot. Thus, the seating spring reduces wear by minimizing axial free play between the vane sectors and the stator casing while allowing differential thermal expansion and contraction during operation. However, it is possible for the tip of the resilient spring arm to work its way radially outward and ultimately lose contact with the outer band. If this were to happen, then the outer band would not be biased against the casing, and the seating spring would not function in its intended manner.
Accordingly, there is a need for a vane sector seating spring that eliminates the possibility of losing contact with the outer band of the vane sector.